1. Field of the Invention
The present invention relates to a circular display device, and more particularly, to a circular display device for displaying an image on an outer surface of a columnar waveguide plate with a projective light source.
2. Description of the Prior Art
Large display devices can be used to communicate information to a large number of people in advertisements. Large outdoor display devices often utilize light emitting diodes (LEDs) to be the light source. However, the maintenance of the large display device costs much due to a large number of LEDs. Otherwise, a television wall also can be utilized for advertisements, but the grid of the television wall due to the partition of televisions decreases the image quality. For solving above-mentioned problems, a 360 degrees circular display device is utilized.
Please refer to FIG. 1. FIG. 1 is a drawing of a display apparatus 10 disclosed in U.S. Pat. No. 5,818,401. The display apparatus 10 includes a pedestal 12, a cylindrical body 14 rotatably mounted on the pedestal 12, and a plurality of LED arrays 16 secured on the wall of the cylindrical body 14. Each LED array 16 includes a plurality of LEDs 18. When the cylindrical body 14 rotates at a speed in which a viewer's eyes cannot distinguish that the individual LED array 16 and the LEDs 18 are sequentially turned on, a viewer sees the corresponding image on the rotating cylindrical body 14 due to the persistence of vision. Please refer to FIG. 2. FIG. 2 is a drawing of a display apparatus 20 disclosed in U.S. Pat. No. 6,335,714. The display apparatus 20 includes a pedestal 22, a cylindrical body 24 rotatably mounted on the pedestal 22, and a plurality of LED sections 26 secured on the wall of the cylindrical body 24. Each LED section 26 includes a plurality of LEDs 28. When the cylindrical body 24 rotates at a speed in which a viewer's eyes cannot distinguish that the individual LED section 26 and the LEDs 28 are sequentially turned on, a viewer sees the corresponding image on the rotating cylindrical body 24 due to the persistence of vision. Generally, the method for displaying images using LEDs has disadvantages of large pixels and non-uniform illumination, decreasing the image quality.